The firA gene, a locus involved in the expression of rifampicin resistance in Escherichia coli. II. Characterisation of bacterial proteins coded by lambdafirA transducing phages.

The firA gene probably codes for an essential component of the transcription machinery in E. coli. Bacterial proteins coded by lambdafirA transducing phages have been examined after infection of a UV-irradiated lambda lysogen, and 2 major fir-specific proteins have been characterized. The larger protein has a molecular weight of 27,000 daltons. The smaller protein, of 17,000 daltons, is produced in a considerable molar excess over the larger protein, is basic and binds strongly to DNA-, to DEAE- and to phospho-cellulose. This protein is clearly visible upon 2-dimensional gel electrophoresis of unfractionated E. coli protein, showing that it is present in the cell in large quantities. Evidence is presented to suggest that this protein may be identical to the Kappa factor of Schäfer and Zillig (1973).